Sealable biaxially orientated polypropylene film with a propective coating sealing against pvdc and acrylate lacquer

ABSTRACT

The invention relates to a multi-layered biaxially orientated polyolefin film comprising a base layer and at least one protective coating. Said protective coating contains, as the main component, one copolymer or terpolymer I, which seals against PVDC and acrylate lacquers and coatings and consists of an olefin and unsaturated carboxylate acids or the esters thereof, and small quantities of wax. The film is provided on one side with a PVDC or acrylate coating so that it can be used as roll-wrap packaging.

[0001] The invention relates to a polyolefin film having improvedsealability to PVDC and acrylate lacquers and coatings.

BACKGROUND OF THE INVENTION

[0002] Foods and other packaged products are frequently sealed inpackaging films. In high-quality packaging, use is made of films whichare coated with a PVDC or acrylate lacquer in order to protect the printand to increase the gloss. A particular form of packaging of this typeis “roll-wrap” packaging, in which flat circular products, such as, forexample, cookies, are introduced in stacks in a single operation into afilm tube which has a longitudinal seal seam on the enveloping surfaceand which has a diameter which matches very precisely. The longitudinalseam seal here can be sealed either with the inside against the insideof the packaging (fin seal) or with the inside against the outside (lapseal).

[0003] The length of the tube is such that its two ends are subsequentlyfolded over the center of the circular end faces from four to twelvetimes and heat-sealed overlapping in this way. Sealing is effected hereboth inside against inside and inside against outside in order toachieve a substantially tightly sealed pack.

[0004] In a particular embodiment, the fin seal can be effected in sucha way that one edge projects slightly over the other edge of the sealedenveloping surface, the fin seal is folded over at the sides, and theprojecting part is sealed with the inside of the tube material againstits outside.

[0005] The packaging material from which roll-wrap packaging of thistype is shaped must be designed in such a way that sealing can beeffected both inside against inside and also inside against outside ofthe film, with sealing advantageously taking place even at low sealingpressures in cases in which fragile products, such as cookies, are to bepacked. In addition to roll-wrap packaging, numerous other packagingforms are known in which similar requirements are made.

[0006] Prior-art packaging which meets these requirements includes BOPPfilms which are provided with a coating of PVDC or acrylic lacquers overthe print and on the opposite side, i.e. on both sides. Depending on thesystem, coatings of this type require the use of solvents, which arepartly released into the environment during drying or are retained bymeans of technical measures and have to be worked up, or require a highapplication rate and thus high usage of materials. This is associatedwith costs for the materials employed and for the provision andoperation of the application systems and the corresponding ancillaryequipment.

[0007] British Application GB 2 223 446 describes a BOPP film whichconsists of at least two layers, with the comparatively thinner layerconsisting of a blend of a material which has low heat seal strength toPVDC and a material which consists of a copolymer of an alkene and anunsaturated monobasic acid or an ester thereof. In preferredembodiments, suitable materials having low heat seal strength to PVDCare high- and low-density polyethylenes, and suitable copolymers arethose of ethylene with acrylic acid esters, where, in particularlypreferred embodiments, these copolymers can comprise unsaturated dibasicacids or anhydrides thereof, such as, for example, maleic anhydride, asfurther monomers. Corresponding copolymers and terpolymers have beendescribed in EP 0 065 898.

[0008] On repetition of British Application GB 2 223 446, it wasobserved that the process described therein results, on use of theformulations indicated therein, in deposits on the heating andstretching rolls of the longitudinal stretching unit of a sequentialBOPP machine to a large extent which is unacceptable for industrialpractice. Variations within the limits of the disclosed teaching broughtno advantage or only a slight advantage with respect to the amount andspeed of the roll coating built up, or the sealing properties wereadversely affected.

[0009] The object of the present invention was therefore to provide abiaxially oriented polyolefin film which is composed of readilyavailable and inexpensive components and is distinguished by the factthat on the one hand it seals, by means of a top layer, to coatings orlacquers based on PVDC or acrylates, and on the other hand can beproduced without the formation of deposits on the rolls of thelongitudinal stretching unit. In addition, the usual service propertiesand optical properties of the film should not be adversely affected.

BRIEF DESCRIPTION OF THE INVENTION

[0010] This object is achieved by a multilayered biaxially orientedpolyolefin film comprising a base layer and at least one first toplayer, where this first top layer comprises at least 80% by weight of acopolymer or terpolymer I and at most 20% by weight of a wax, the datain % by weight in each case being based on the weight of the first toplayer. The copolymer or terpolymer I is built up from an olefin and anunsaturated carboxylic acid or esters thereof.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Within the scope of the present invention, it has been found,surprisingly, that a small amount of wax in the first top layercomprising copolymer or terpolymer I prevents roll deposits and at thesame time the sealing properties of the film are not adversely affected.In particular, it has been found that a top layer built up only from thesaid copolymer or terpolymer I sticks to the rolls or forms depositsduring production in such a way that handling of the material isvirtually impossible.

[0012] The first top-layer composition according to the inventionexhibits the desired sealing properties against itself (AA or BBsealing) and against PVDC- or acrylic-based lacquers (AB sealing), asare necessary for roll-wrap packaging. On use in accordance with theinvention for roll-wrap packaging, PVDC or acrylic coatings on bothsides of the film are therefore unnecessary.

[0013] Surprisingly, the film according to the invention has very goodprocessing properties and does not exhibit any undesired pick-off duringunrolling of the coated film, i.e. the adhesion of the first top layerto the PVDC or acrylate coating is not so great that this coating isdetached from the opposite surface and remains adhering to the first toplayer.

[0014] The first top layer comprises, as constituents which areessential to the invention, a copolymer or terpolymer I comprising anolefin and an unsaturated carboxylic acid or esters thereof and a wax.If desired, the first top layer additionally comprises antiblockingagents and/or a polyethylene. In general, the first top layer comprisesat least 80% by weight, preferably from 90 to 99.5% by weight, inparticular from 96 to 99% by weight, of the copolymer or terpolymer Iand at most 20% by weight, preferably from 0.5 to 10% by weight, inparticular from 1 to 4% by weight, of the wax.

[0015] The copolymer or terpolymer I is essential for sealing of thefirst top layer to PVDC and/or acrylate lacquers and coatings. Suitablecopolymers or terpolymers I are built up from olefins and unsaturatedcarboxylic acids or esters thereof as monomers. Olefins are, forexample, ethylene, propylene or 1-butene, if desired also higherhomologs, such as, for example, hexene or octene. Unsaturated carboxylicacids include unsaturated mono- and dicarboxylic acids and esters oranhydrides thereof. Preferred unsaturated carboxylic acids are acrylicacid or methacrylic acid and esters thereof. In principle, the copolymeror terpolymer I can be built up from different olefins and differentunsaturated carboxylic acids or esters/anhydrides thereof. Copolymers Icomprising ethylene and acrylic acid esters are particularlyadvantageous.

[0016] Terpolymers I are generally built up from the above-mentionedolefins and an unsaturated monocarboxylic acid or an ester thereof andan unsaturated dicarboxylic acid or an ester/anhydride thereof.Preferred unsaturated dicarboxylic acids or anhydride thereof are maleicacid or maleic anhydride. Terpolymers comprising ethylene, acrylic acidor methacrylic acid or esters thereof and maleic anhydride areparticularly advantageous.

[0017] The esters of the unsaturated carboxylic acids described arederived from one or more lower alcohols. Methyl, ethyl, n-propyl,i-propyl, n-butyl, i-butyl, sec-butyl or tert-butyl esters, for example,are suitable.

[0018] The composition comprising the respective monomers can varywithin the limits described below. Copolymers I generally comprise atleast 60% by weight, preferably from 70 to 97% by weight, of olefin,preferably ethylene, and at most 40% by weight, preferably from 3 to 30%by weight, of unsaturated carboxylic acids or esters thereof, preferablyacrylic acid or methacrylic acid or esters thereof. Terpolymers Igenerally comprise from 65 to 96% by weight, preferably from 72 to 93%by weight, of olefin, preferably ethylene, and from 3 to 34% by weight,preferably from 5 to 26% by weight, of unsaturated carboxylic acids oresters thereof, preferably acrylic acid or methacrylic acid or estersthereof, and from 1 to 32% by weight, preferably from 2 to 23% byweight, of unsaturated dicarboxylic acid or an ester/anhydride thereof,preferably maleic anhydride.

[0019] The above-described copolymers or terpolymers I in the first toplayer generally have a melting point of from 40 to 120° C., preferablyfrom 60 to 100° C. The Vicat point is preferably in the range from 30 to90° C. The melt flow index is generally from 0.1 to 20 g/10 min (190°C., 21.6 N), preferably from 0.1 to 15 g/10 min.

[0020] As a further component which is essential to the invention, thefirst top layer comprises a wax, preferably polyethylene waxes, orparaffins. Polyethylene waxes are low-molecular-weight polymers whichare essentially built up from ethylene units and are partly or highlycrystalline. The polymer chains from the ethylene units are elongatechains, which may be branched, with relatively short side chainspredominating. In general, polyethylene waxes are prepared by directpolymerization of ethylene, if desired with use of regulators, or bydepolymerization of polyethylenes of relatively high molecular weight.The polyethylene waxes preferably have a mean molecular weight Mn(number average) of from 200 to 5000, preferably from 400 to 2000,particularly preferably from 400 to 1000, and preferably have amolecular weight distribution (polydispersity) Mw/Mn of less than 3,preferably from 1 to 2. The melting point is generally in the range from70 to 150° C., preferably from 80 to 100° C.

[0021] Paraffins include macrocrystalline paraffins (paraffin waxes) andmicrocrystalline paraffins (microwaxes). Macrocrystalline paraffins areobtained from vacuum distillate fractions on conversion thereof intolubricating oils. Microcrystalline paraffins originate from the residuesof vacuum distillation and the sediments of paraffinic crude oils(deposition paraffins). Macrocrystalline paraffins consist predominantlyof n-paraffins which additionally contain isoparaffins, naphtenes andalkylaromatic compounds, depending on the degree of refining.Microcrystalline paraffins consist of a mixture of hydrocarbons whichare predominantly solid at room temperature. In contrast to thesituation in macrocrystalline paraffins, isoparaffins and naphtenicparaffins predominate. Microcrystalline paraffins are distinguished bythe presence of crystallization-inhibiting, highly branched isoparaffinsand naphthenes. For the purposes of the invention, paraffins having amelting point of from 60 to 100° C., preferably from 60 to 85° C., areparticularly suitable.

[0022] In a further embodiment, the first top layer may additionallycomprise a further component which is compatible with the copolymer orterpolymer I and itself has a low heat seal strength to PVDC or acryliclacquers and coatings. The proportion of components of this type isgenerally between 0 and 30% by weight, preferably from 1 to 20% byweight, in particular from 3 to 10% by weight, with the proportion ofcopolymer or terpolymer I in the composition of the top layer beingreduced correspondingly. Suitable components of this type arepolyethylenes, polypropylenes, polystyrene, polyesters or polyamides.Preference is given to polyethylenes, with both linear and branchedpolyethylenes in principle being suitable, for example LLDPE, LDPE orHDPE. The suitable polyethylenes have a significantly higher molecularweight than the polyethylene waxes. The number average Mn is generallygreater than 10,000 and is preferably from 30,000 to 300,000, inparticular from 40,000 to 200,000. The melting point of the preferredpolyethylenes is generally 90-150° C., preferably 110-140° C. The meltflow index is generally from 1 to 50 g/10 min, preferably from 10 to 30g/10 min. Embodiments which additionally comprise polyethylenes are evenmore advantageous with respect to the tendency to stick during theproduction process, and the detachment of PVDC or acrylate coating whichoccurs is avoided even more reliably. It is surprising that thepolyethylenes, which are similar in structure to the waxes, furtherincrease the advantageous action of the waxes, whereas a furtherincrease in the wax content does not achieve this action.

[0023] The first top layer may additionally comprise conventionaladditives, such as neutralizers, stabilizers, antistatics, antiblockingagents and/or lubricants, in effective amounts in each case. The data in% by weight below in each case relate to the weight of the first toplayer. Particular preference is given to embodiments which additionallycomprise antiblocking agents in the first top layer.

[0024] Suitable antiblocking agents are inorganic additives, such assilicon dioxide, calcium carbonate, magnesium silicate, aluminumsilicate, calcium phosphate and the like, and/or incompatible organicpolymers, such as polyamides, polyesters, polycarbonates and the like,or crosslinked polymers, such as crosslinked polymethyl methacrylate orcrosslinked silicone oils. Silicon dioxide and calcium carbonate arepreferred. The mean particle size is between 1 and 6 μm, in particularbetween 2 and 5 μm. The effective amount of antiblocking agent is in therange from 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, inparticular from 0.8 to 2% by weight. In addition, the antiblocking agenthas a favorable action with respect to low pick-off.

[0025] In a preferred embodiment, the surface of the first top layer iscorona-, plasma- or flame-treated.

[0026] In accordance with the invention, films provided with the firsttop layer described above have heat seal strengths to PVDC lacquers ofgreater than 1.5 N/15 mm, measured at 110° C./sealing pressure of 10N/mm²/sealing time of 0.5 sec. (Indicate range for heat seal strength)

[0027] The thickness of the first top layer is generally greater than0.3 μm and is preferably in the range from 0.5 to 5 μm, in particularfrom 1 to 3 μm.

[0028] The above-described first top layer having the compositionaccording to the invention can advantageously be applied to transparentor opaque base layers. It has furthermore been found that opaqueembodiments of the film according to the invention, in particular thosehaving a vacuole-containing base layer, surprisingly have particularlygood sealing properties, in particular also in the case of AB seals. Forthe purposes of the present invention, ‘opaque film’ means anon-transparent film whose light transparency (ASTM-D 1003-77) is atmost 70%, preferably at most 50%.

[0029] For transparent embodiments, the base layer of the film generallycomprises at least 85% by weight, preferably from 90 to <100% by weight,in particular from 95 to 99% by weight, in each case based on the baselayer, of a polyolefin. Polyolefins are, for example, polyethylenes,polypropylenes, polybutylenes or copolymers of olefins having from twoto eight carbon atoms, amongst which polyethylenes and polypropylenesare preferred.

[0030] In general, the propylene polymer comprises at least 90% byweight, preferably from 94 to 100% by weight, in particular from 98 to<100% by weight, of propylene. The corresponding comonomer content of atmost 10% by weight or from 0 to 6% by weight or from 0 to 2% by weightrespectively generally consists, if present, of ethylene. The data in %by weight are in each case based on the propylene polymer.

[0031] Preference is given to isotactic propylene homopolymers having amelting 20 point of from 140 to 170° C., preferably from 155 to 165° C.,and a melt flow index (measurement DIN 53 735 at a load of 21.6 N and230° C.) of from 1.0 to 10 g/10 min, preferably from 1.5 to 6.5 g/10min. The n-heptane-soluble content of the polymer is generally from 1 to10% by weight, preferably from 2 to 5% by weight, based on the startingpolymer. The molecular weight distribution of the propylene polymer canvary. The ratio between the weight average M_(w) and the number averageM_(n) is generally between 1 and 15, preferably from 2 to 10, veryparticularly preferably from 2 to 6. Such a narrow molecular weightdistribution of the propylene homopolymer of the base layer is achieved,for example, by peroxidic degradation thereof or by preparation of thepolypropylene by means of suitable metallocene catalysts.

[0032] In a preferred embodiment, the base layer is opaque due to theaddition of fillers. In general, the base layer in this embodimentcomprises at least 70% by weight, preferably from 75 to 99% by weight,in particular from 80 to 98% by weight, in each case based on the weightof the base layer, of the above-described polyolefins or propylenepolymers, with the propylene homopolymers described likewise beingpreferred.

[0033] The opaque base layer comprises fillers in a maximum amount of30% by weight, preferably from 1 to 25% by weight, in particular from 2to 20% by weight, based on the weight of the base layer. For thepurposes of the present invention, fillers are pigments and/orvacuole-initiating particles.

[0034] For the purposes of the present invention, pigments areincompatible particles which essentially do not result in vacuoleformation when the film is stretched. The coloring action of thepigments is caused by the particles themselves. In general, “pigments”have a mean particle diameter of from 0.01 to a maximum of 1 μm,preferably from 0.01 to 0.7 μm, in particular from 0.01 to 0.4 μm.Pigments include both so-called “white pigments”, which color the filmswhite, and also “colored pigments”, which give the film a colored orblack color. Conventional pigments are materials such as, for example,aluminum oxide, aluminum sulfate, barium sulfate, calcium carbonate,magnesium carbonate, silicates, such as aluminum silicate (kaolin clay)and magnesium silicate (talc), silicon dioxide and titanium dioxide, ofwhich preference is given to the use of white pigments, such as calciumcarbonate, silicon dioxide, titanium dioxide and barium sulfate.

[0035] The titanium dioxide particles generally comprise at least 95% byweight of rutile and are preferably employed with a coating of inorganicoxides and/or of organic compounds containing polar and nonpolar groups.TiO2 coatings of this type are known in the prior art.

[0036] For the purposes of the present invention, “vacuole-initiatingfillers” are solid particles which are incompatible with the polymermatrix and result in the formation of vacuole-like cavities when thefilms are stretched, with the size, nature and number of the vacuolesbeing dependent on the size and amount of the solid particles and thestretching conditions, such as stretching ratio and stretchingtemperature. The vacuoles reduce the density and give the films acharacteristic mother-of-pearl-like opaque appearance caused by lightscattering at the “vacuole/polymer matrix” interfaces. Light scatteringat the solid particles themselves generally makes relatively littlecontribution towards the opacity of the film. In general, thevacuole-initiating fillers have a minimum size of 1 μm in order to givean effective, i.e. opacifying amount of vacuoles. In general, the meanparticle diameter of the particles is from 1 to 6 μm, preferably from1.5 to 5 μm. The chemical character of the particles plays a secondaryrole.

[0037] Conventional vacuole-initiating fillers are inorganic and/ororganic, polypropylene-incompatible materials, such as aluminum oxide,aluminum sulfate, barium sulfate, calcium carbonate, magnesiumcarbonate, silicates, such as aluminum silicate (kaolin clay) andmagnesium silicate (talc), and silicon dioxide, of which calciumcarbonate and silicon dioxide are preferably employed. Suitable organicfillers are the conventionally used polymers which are incompatible withthe polymer of the base layer, in particular those such as HDPE,copolymers of cyclic olefins, such as norbornene or tetracyclododecenewith ethylene or propene, polyesters, polystyrenes, polyamides andhalogenated organic polymers, preference being given to polyesters, suchas, for example, polybutylene terephthalates. For the purposes of thepresent invention, “incompatible materials or incompatible polymers”means that the material or polymer is present in the film in the form ofa separate particle or separate phase.

[0038] The opaque base layer comprises pigments in an amount of from 0.5to 10% by weight, preferably from 1 to 8% by weight, in particular from1 to 5% by weight. Vacuole-initiating fillers are present in an amountof from 0.5 to 30% by weight, preferably from 1 to 15% by weight, inparticular from 1 to 10% by weight. The data are based on the weight ofthe base layer.

[0039] The density of the opaque embodiments can vary in broad rangesand is between 0.5 and 0.96 g/cm³. A vacuole-containing base layerreduces the density of the film, which is then in the range from 0.55 to0.8 g/cm³, preferably from 0.6 to 0.75 g/cm³. Films having avacuole-containing base layer are particularly advantageous with respectto sealing.

[0040] In addition, the base layer, both in a transparent and in anopaque embodiment, can comprise conventional additives, such asneutralizers, stabilizers, antistatics and/or lubricants, in effectiveamounts in each case. The data in % by weight below are in each casebased on the weight of the base layer.

[0041] Preferred antistatics are alkali metal alkanesulfonates,polyether-modified, i.e., ethoxylated and/or propoxylatedpolydiorganosiloxanes (polydialkylsiloxanes, polyalkylphenylsiloxanesand the like) and/or essentially straight-chain and saturated aliphatic,tertiary amines containing an aliphatic radical having from 10 to 20carbon atoms which are substituted by w-hydroxy-(C₁-C₄)alkyl groups,where N,N-bis(2-hydroxyethyl)alkylamines having from 10 to 20 carbonatoms, preferably from 12 to 18 carbon atoms, in the alkyl radical areparticularly suitable. The effective amount of antistatic is in therange from 0.05 to 0.5% by weight.

[0042] Lubricants are higher aliphatic acid amides, higher aliphaticacid esters, waxes and metal soaps, as well as polydimethylsiloxanes.The effective amount of lubricant is in the range from 0.01 to 3% byweight, preferably from 0.02 to 1% by weight. Particularly suitable isthe addition of higher aliphatic acid amides in the range from 0.01 to0.25% by weight in the base layer. Particularly suitable aliphatic acidamides are erucamide and stearylamide. The addition ofpolydimethylsiloxanes in the range from 0.02 to 2.0% by weight ispreferred, in particular polydimethylsiloxanes having a viscosity from5000 to 1,000,000 mm²/s.

[0043] Stabilizers which can be employed are the conventional compoundswhich have a stabilizing action for polymers of ethylene, propylene andother a-olefins. Their added amount is between 0.05 and 2% by weight.Particularly suitable are phenolic and phosphitic stabilizers. Phenolicstabilizers having a molecular weight of greater than 500 g/mol arepreferred, in particular pentaerythrityltetrakis-3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate or1,3,5-trimethyl-2,4,6-tris(3,5-di-tertiary-butyl-4-hydroxybenzyl)benzene.Phenolic stabilizers are employed alone here in an amount of from 0.1 to0.6% by weight, in particular from 0.1 to 0.3% by weight, and phenolicand phosphitic stabilizers are employed in the ratio from 1:4 to 2:1 andin a total amount of from 0.1 to 0.4% by weight, in particular from 0.1to 0.25% by weight.

[0044] Neutralizers are preferably dihydrotalcite, calcium stearateand/or calcium carbonate having a mean particle size of at most 0.7 μm,an absolute particle size of less than 10 μm and a specific surface areaof at least 40 m²/g. (What are usual amounts?)

[0045] For two-layered embodiments, which have only one first top layer,it is preferred for the outer surface of the base layer to besurface-treated by means of corona, plasma or flame.

[0046] The polyolefin film according to the invention preferably has asecond top layer which exhibits good adhesion to conventional printinginks, adhesives, and PVDC- or acrylic-based coatings and/or lacquers.This second top layer is preferably applied to the opposite surface ofthe base layer and is referred to below as the “second top layer”. Forfurther improvement of the adhesion, it is preferred to carry out acorona, plasma or flame treatment of the surface of the second toplayer.

[0047] The second top layer is generally built up from polymers ofolefins having from 2 to 10 carbon atoms. The second top layer generallycomprises from 95 to 100% by weight of polyolefin, preferably from 98 to<100% by weight of polyolefin, in each case based on the weight of thetop layer(s).

[0048] Examples of suitable olefinic polymers of the top layer(s) arepropylene homopolymers, copolymers or terpolymers II comprisingethylene, propylene and/or butylene units, or mixtures of the saidpolymers. These copolymers or terpolymers II do not contain anycarboxylic acid monomers. They are polyolefins. Of these, preferredpolymers are

[0049] random ethylene-propylene copolymers having an ethylene contentof from 1 to 10% by weight, preferably from 2.5 to 8% by weight, or

[0050] random propylene-1-butylene copolymers having a butylene contentof from 2 to 25% by weight, preferably from 4 to 20% by weight, or

[0051] random ethylene-propylene-1-butylene terpolymers having anethylene content of from 1 to 10% by weight and a 1-butylene content offrom 2 to 20% by weight, or

[0052] a mixture or blend of ethylene-propylene-1-butylene terpolymersand propylene-1-butylene copolymers having an ethylene content of from0.1 to 7% by weight and a propylene content of from 50 to 90% by weightand a 1-butylene content of from 10 to 40% by weight. The data in % byweight are in each case based on the weight of the polymer.

[0053] The above-described copolymers and/or terpolymers II employed inthe second top layer, which are built up exclusively from olefins,generally have a melt flow index of from 1.5 to 30 g/10 min, preferablyfrom 3 to 15 g/10 min. The melting point is in the range from 120 to140° C. The above-described blend of copolymers and terpolymers II has amelt flow index of from 5 to 9 g/10 min and a melting point of from 120to 150° C. All the above-mentioned melt flow indices are measured at230° C. and a force of 21.6 N (DIN 53 735). If desired, all top-layerpolymers described above may be peroxidically degraded, with thedegradation factor generally being in the range from 1 to 15, preferablyfrom 1 to 8.

[0054] If desired, the additives described above, such as antistatics,neutralizers, lubricants, and/or stabilizers, and, if desired,additionally antiblocking agents, can be added to the second toplayer(s). The data in % by weight are then based correspondingly on theweight of the second top layer.

[0055] Suitable antiblocking agents have already been described inconnection with the first top layer. These antiblocking agents are alsosuitable for the second top layer. The preferred amount of antiblockingagent for the second top layer is in the range from 0.1 to 2% by weight,preferably from 0.1 to 0.8% by weight.

[0056] The thickness of the second top layer is greater than 0.1 μm andis preferably in the range from 0.1 to 5 μm, in particular from 0.5 to 3μm.

[0057] The film according to the invention includes at least the baselayer described above and the first top layer, comprising copolymer orterpolymer I and wax. If desired, a second top layer of purely olefinicpolymers is applied to the opposite surface. If desired, interlayer(s)may also be present on one or both sides between the base layer and thetop layer(s).

[0058] The interlayer(s) can be built up from the olefinic polymers,preferably propylene polymers, described for the base layer or for thetop layers. The interlayer(s) may comprise the conventional additivesdescribed for the individual layers, such as antistatics, neutralizers,lubricants and/or stabilizers. In a preferred embodiment, wax canlikewise be added to the interlayer that is arranged between the baselayer and the first top layer. Suitable waxes are the waxes describedabove for the first top layer. The wax content in the interlayer is inthe region of at most 20% by weight, preferably from 0.5 to 10% byweight, in particular from 1 to 4% by weight, in each case based on theweight of the interlayer. The thickness of this interlayer is greaterthan 0.5 μm and is preferably in the range from 0.6 to 4 μm, inparticular from 0.8 to 3 μm.

[0059] For embodiments having an opaque appearance, the interlayerbetween the second top layer and the base layer may comprisevacuole-initiating fillers and/or pigments. The thickness of this opaqueinterlayer is greater than 0.3 μm and is preferably in the range from1.0 to 15 μm, in particular from 1.5 to 10 μm.

[0060] The total thickness of the polypropylene film according to theinvention can vary within broad limits and depends on the intended use.It is preferably from 4 to 60 μm, in particular from 5 to 30 μm,preferably from 6 to 25 μm, with the base layer making up from about 40to 99% of the total film thickness.

[0061] The invention furthermore relates to a process for the productionof the polyolefin film according to the invention by the coextrusionprocess, which is known per se. This process is carried out bycoextruding the melts corresponding to the individual layers of the filmthrough a flat-film die, taking off the resultant film over one or moreroll(s) for solidification, subsequently stretching (orienting) thefilm, heat-setting the stretched film and, if desired, plasma-, corona-or flame-treating the surface layer intended for the treatment.

[0062] Biaxial stretching (orientation) is carried out sequentially orsimultaneously. The sequential stretching is generally carried outconsecutively, with consecutive biaxial stretching, in which stretchingis firstly carried out longitudinally (in the machine direction) andthen transversely (perpendicular to the machine direction), beingpreferred. The film production is described further using the example offlat film extrusion with subsequent sequential stretching.

[0063] Firstly, as is usual in the extrusion process, the polymer or thepolymer mixture of the individual layers is compressed and liquefied inan extruder, it being possible for any additives already to be presentin the polymer or polymer mixture. The melts are then forcedsimultaneously through a flat-film die (slot die), and the extrudedmultilayer film is taken off over one or more take-off rolls at atemperature of from 10 to 100° C., preferably from 10 to 50° C., duringwhich it cools and solidifies.

[0064] The film obtained in this way is then stretched longitudinallyand transversely to the extrusion direction, which results inorientation of the molecule chains. The longitudinal stretching ispreferably carried out at a temperature of from 70 to 120° C.,advantageously with the aid of two rolls running at different speedscorresponding to the target stretching ratio, and the transversestretching is preferably carried out at a temperature of from 120 to180° C. with the aid of an appropriate tenter frame. The longitudinalstretching ratios are in the range from 3 to 8, preferably from 4 to 6.The transverse stretching ratios are in the range from 5 to 10,preferably from 7 to 9.

[0065] The stretching of the film is followed by heat-setting (heattreatment) thereof, in which the film is held at a temperature from 100to 160° C. for from about 0.1 to 10 seconds. The film is subsequentlywound up in a conventional manner by means of a wind-up device.

[0066] After the biaxial stretching, one or both surface(s) of the filmis (are) preferably plasma-, corona- or flame-treated by one of theknown methods. The treatment intensity is generally in the range from 35to 50 mN/m, preferably from 37 to 45 mN/m.

[0067] In the case of corona treatment, an advantageous procedure is topass the film between two conductor elements serving as electrodes, withsuch a high voltage, usually an alternating voltage (from about 5 to 20kV and from 5 to 30 kHz), being applied between the electrodes thatspray or corona discharges are able to occur. Due to the spray or coronadischarge, the air above the film surface ionizes and reacts with themolecules of the film surface, causing the formation of polar inclusionsin the essentially non-polar polymer matrix.

[0068] The raw materials and films were characterized using thefollowing measurement methods:

[0069] Melt Flow Index

[0070] The melt flow index was measured in accordance with DIN 53 735 ata load of 21.6 N and 230 C.

[0071] Melting Point

[0072] DSC measurement, maximum of the melting curve, heating rate 20C/min.

[0073] Haze

[0074] The haze of the film was measured in accordance with ASTM-D1003-52.

[0075] Gloss

[0076] The gloss was determined in accordance with DIN 67 530. Thereflector value was measured as an optical parameter for the surface ofa film. In accordance with the standards ASTM-D 523-78 and ISO 2813, theangle of incidence was set at 600 or 850. A light beam hits the planartest surface at the set angle of incidence and is reflected or scatteredthereby. The light beams incident on the photoelectronic receiver aredisplayed as a proportional electrical quantity. The measurement valueis dimensionless and must be specified together with the angle ofincidence.

[0077] Surface Tension

[0078] The surface tension was determined by the ink method (DIN 53364).

[0079] Printability

[0080] The corona-treated films were printed 14 days after production(short-term assessment) and 6 months after production (long-termassessment). The ink adhesion was assessed by means of the adhesive-tapetest. If little ink was removable by means of the adhesive tape, the inkadhesion was assessed as being moderate, and if a significant amount ofink was removable, it was assessed as being poor.

[0081] Determination of the Blocking Behavior:

[0082] One or more film samples which are to be investigated withrespect to their blocking behavior are stacked alternately with a filmsample which has been coated on its surface with PVDC or acrylatelacquer, in such a way that the outside of the film sample to be testedis in contact with the PVDC lacquer or acrylate lacquer. In order to beable to clamp any film pieces which may block against one another in thetensile testing machine, a strip with a width of a few centimeters is ineach case covered, for example with paper. If the film sample itselfcarries the PVDC or acrylate lacquer, every second contact surface iscovered completely in order to enable the film samples to be separatedbetter for the purposes of measurement.

[0083] The stack of samples is pressed for 24 hours at room temperatureunder a pressure of 100 N/cm² by means of a lever press. The filmsamples are then separated, cut into strips with a width of 30 mm andclamped in a tensile testing machine (for example Zwick 1120.25) in sucha way that the film sample to be investigated with respect to itsblocking behavior and the film sample which is coated on its surfacewith PVDC or acrylate lacquer are separated from one another at an angleof twice 90°. During this operation, the force needed to separate thefilm pieces is measured. The mean of three measurements and the extentof any transfer of PVDC or acrylate lacquer to the film sample areemployed for the assessment.

[0084] Molecular Weight Determination

[0085] The mean molecular weights Mw and Mn and the mean molecularweight dispersity Mw/Mn were determined in accordance with DIN 55 672,Part 1, by means of gel permeation chromatography. Instead of THF,ortho-dichlorobenzene was used as eluent. Since the olefinic polymers tobe investigated are insoluble at room temperature, the entiremeasurement is carried out at elevated temperature (>>135° C.).

EXAMPLE 1

[0086] A transparent three-layered film consisting of the base layer Band first and second top layers with a total thickness of 30 μm wasproduced by coextrusion and subsequent stepwise orientation in thelongitudinal and transverse direction. The first top layer had athickness of 2.0 μm and the second top layer had a thickness of 0.7 μm.B base layer: 99.58% by weight of propylene homopolymer having a meltingpoint of 165° C. and a melt flow index of 3.4 g/10 min and a chainisotaxicity index of 94% 0.12% by weight of erucamide 0.14% by weight ofArmostat 300 0.03% by weight of neutralizer (CaCO₃) 0.13% by weight ofstabilizer (Irganox) First top layer: 89.0% by weight of a terpolymer ofethylene, ethyl acrylate and maleic anhydride having an ethylene contentof 91% by weight, an ethyl acrylate content of 5% by weight and a maleicanhydride content of 4% by weight and having a melt flow index of 5.0g/10 mm [at 190° C., 21.6N]. 1.0% by weight of SiO₂ as antiblockingagent having a mean particle size of 4 μm 10.0% by weight of amicrocrystalline wax having a melting point of 76-81° C. and a viscosityof 13-18 mm²/s at 98.89° C. Second top layer: 99.54% by weight of arandom copolymer of ethylene and propylene having a melt flow index of6.0 g/10 min and an ethylene content of 6% by weight, based on thecopolymer 0.22% by weight of SiO₂ as antiblocking agent having a meanparticle size of 4 μm 0.20% by weight of stabilizer (Irganox/Irgafos)0.04% by weight of neutralizer (CaCO₃).

[0087] The production conditions in the individual process steps were asfollows: Extrusion: Temperatures Base layer: 260° C. Top layers A: 240°C. Top layer C: 230° C. Temperature of the take-off roll:  20° C.Longitudinal stretching: Temperature: 100° C. Longitudinal stretchingratio: 4.5 Transverse stretching: Temperature: 165° C. Transversestretching ratio: 9 Setting: Temperature: 140° C. Convergence: 10%

[0088] The transverse stretching ratio I_(T)=9 is an effective value.This effective value is calculated from the final film width B reducedby twice the hem width b, divided by the width of the longitudinallystretched film C, likewise reduced by twice the hem width b.

EXAMPLE 2

[0089] A three-layered film was produced as described in Example 1. Incontrast to Example 1, 5.1% by weight of calcium carbonate having a meanparticle diameter of 2 μm as vacuole-initiating particles (chalk) and2.8% by weight of titanium dioxide as pigment (rutile) were additionallyincorporated into the base layer. The polypropylene content was reducedcorrespondingly. The production conditions in the individual processsteps were as in Example 1. The film was white and opaque.

EXAMPLE 3

[0090] A three-layered white, opaque film was produced as described inExample 2. In contrast to Example 2, 10% by weight of a polyethylene waxhaving a molecular weight (number average) of 2000 was used instead of10% by weight of paraffin wax in top layer C. The production conditionsin the individual process steps were as in Example 2.

EXAMPLE 4

[0091] A three-layered white, opaque film was produced as described inExample 3. In contrast to Example 3, 5% by weight of a polyethylene waxhaving a molecular weight Mn (number average) of 655 were used insteadof 10% by weight of the polyethylene wax having an Mn of 2000 in toplayer C. The proportion of terpolymer in top layer C was increasedcorrespondingly. The production conditions in the individual processsteps were as in Example 3.

EXAMPLE 5

[0092] A three-layered white, opaque film was produced as described inExample 4. In contrast to Example 4, 5% by weight of an HDPE having amelting point of 133° C. and a density of 0.957 g/cm³ and an MFI of 15g/10 min (190° C./21.6 N) were additionally added to top layer C. Theproduction conditions in the individual process steps were as in Example4.

EXAMPLE 6

[0093] A three-layered white, opaque film was produced as described inExample 5. In contrast to Example 5, the content of HDPE was increasedfrom 5 to 10% by weight and the content of SiO2 was reduced from 1 to0.5% by weight. The content of terpolymer was adjusted correspondingly.The production conditions in the individual process steps were as inExample 5.

EXAMPLE 7

[0094] A three-layered white, opaque film was produced as described inExample 6. In contrast to Example 6, top layer C now contained no SiO2.The content of terpolymer was adjusted correspondingly. The productionconditions in the individual process steps were as in Example 6.

EXAMPLE 8

[0095] A three-layered white, opaque film was produced as described inExample 5. In contrast to Example 5, a copolymer of ethylene and ethylacrylate (without maleic anhydride) having an ethylene content of 96% byweight and an ethyl acrylate content of 4% by weight was used instead ofa terpolymer. The melt flow index of the copolymer was 5.0 g/l 0 min [at190° C., 21.6 N]. The production conditions in the individual processsteps were as in Example 5.

COMPARATIVE EXAMPLE 1

[0096] A three-layered white, opaque film was produced as described inExample 5. In contrast to Example 5, layer C now contained no wax. Thecontent of terpolymer was adjusted correspondingly. The productionconditions in the individual process steps were as in Example 5.

COMPARATIVE EXAMPLE 2

[0097] A three-layered white, opaque film was produced as described inExample 5. In contrast to Example 5, top layer C now contained anethylene-propylene copolymer having a melt flow index of 6 g/10 min andan ethylene content of 6% by weight instead of the ethyl acrylatecopolymer described. The production conditions in the individual processsteps were as in Example 5.

COMPARATIVE EXAMPLE 3

[0098] A three-layered white, opaque film was produced as described inExample 5. In contrast to Example 5, top layer C now contained no waxand no HDPE. The content of terpolymer was adjusted correspondingly. Theproduction conditions in the individual process steps were as in Example5.

[0099] The films in accordance with the examples all exhibit goodsealing properties to acrylate coatings and PVDC lacquers and tothemselves. The films do not stick to the rolls during the productionprocess and can be handled easily even during later processing. Duringunwinding of the coated rolls, surfaces in contact can readily beseparated from one another. No or only little pick-off occurs, i.e. theacrylate or PVDC coating does not remain adhering to the surface of thefirst top layer. The films are very well suited for roll-wrap packaging.

[0100] Although the film according to Comparative Example 1 exhibits thedesired sealing to PVDC or acrylate coatings, severe pick-off occurs,however, during unrolling of the coated film, causing the function ofthe coating to be considerably impaired.

[0101] The film according to Comparative Example 2 exhibits no sealingto the PVDC or acrylate coatings.

[0102] The film according to Comparative Example 3 can only be producedunder extremely difficult conditions. The film exhibits a very strongtendency to stick to the rolls. The pick-off during unwinding of thecoated film is considerable. The film is de facto, unsuitable for usefor the desired application.

1. Multilayered, biaxially oriented polyolefin film comprising a baselayer and at least one first top layer, wherein this first top layercomprises at least about 80% by weight of a copolymer or terpolymerbuilt up from an olefin and an unsaturated carboxylic acid or estersthereof and at most 20% by weight of a wax, the data in % by weight ineach case being based on the weight of the first top layer. 2.Polyolefin film according to claim 1, wherein the wax is a polyethylenewax or a macrocrystalline paraffin (paraffin wax) or a microcrystallinewax (microwax) and has a mean molecular weight Mn (number average) offrom about 200 to about
 5000. 3. Polyolefin film according to claim 2,wherein the wax has a mean molecular weight Mn (number average) of fromabout 200 to about
 1000. 4. Polyolefin film according to claim 1 whereinthe wax is a polyethylene wax having a ratio between the weight averagemolecular weight and the number average molecular weight Mw/Mn of fromabout 1 to
 2. 5. Polyolefin film according to claim 1, wherein the waxis present in the top layer in an amount of from about 0.5 to about 10%by weight.
 6. Polyolefin film according to claim 5, wherein the wax ispresent in the top layer in an amount of from about 1 to about 4% byweight.
 7. Polyolefin film according to claim 1, wherein the wax has amelting point of from about 70 to about 120° C.
 8. Polyolefin filmaccording to claim 1, wherein the first top layer comprises from aboutabout 90 to about 99.5% by weight of the copolymer or terpolymer. 9.Polyolefin film according to claim 1, wherein the unsaturated carboxylicacid is acrylic acid or methacrylic acid and the olefin is selected fromone or more of ethylene, propylene and butylene.
 10. Polyolefin filmaccording to claim 1, wherein the unsaturated carboxylic acid is maleicacid.
 11. Polyolefin film according to claim 1, wherein the copolymercomprises more than about 65% by weight of ethylene units and at mostabout 35% by weight of unsaturated monocarboxylic acid units or estersthereof.
 12. Polyolefin film according to claim 1, wherein theterpolymer comprises from about 65 to about 96% by weight of ethyleneunits and from about 5 to about 20% by weight of unsaturatedmonocarboxylic acid units or esters thereof and from <about 1 to about10% by weight of unsaturated dicarboxylic acid units or anhydridesthereof.
 13. Polyolefin film according to claim 1, wherein theunsaturated carboxylic acid is an acrylic acid ester.
 14. Polyolefinfilm according to claim 13, wherein the unsaturated carboxylic acidester is acrylic acid methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, sec-butyl or tert-butyl ester.
 15. Polyolefin film according toclaim 1, wherein the unsaturated carboxylic acid is maleic anhydride.16. Polyolefin film according to claim 1, wherein the top layercomprises antiblocking agent.
 17. Polyolefin film according to claim 16,wherein the antiblocking agent comprises from about 1 to about 5% byweight.
 18. Polyolefin film according to claim 1, wherein the top layeradditionally comprises a further component.
 19. Polyolefin filmaccording to claim 18, wherein the further component comprises a linearor branched polyethylene of low (LLD-PE, LD-PE), medium or high (HD-PE)density, polypropylene, polystyrene, polyester or polyamide. 20.Polyolefin film according to claim 18, wherein the top layer comprisesthe further component in an amount of from about 1 to about 20% byweight.
 21. Polyolefin film according to claim 1, wherein the first toplayer has been corona-, plasma- or flame-treated.
 22. Polyolefin filmaccording to claim 1, wherein the film has a second top layer built upfrom a-olefinic polymers on the opposite side of the base layer from thefirst top layer.
 23. Polyolefin film according to claim 22, wherein thesurface of the second top layer has been corona-, plasma- orflame-treated.
 24. Polyolefin film according to claim 22, wherein thesecond top layer comprises antiblocking agent.
 25. Polyolefin filmaccording to claim 24, wherein the antiblocking agent is SiO₂. 26.Polyolefin film according to claim 1 or 22, wherein an interlayer ofa-olefinic polymers is applied between the base layer and the first toplayer or the base layer and the second top layer or the base layer andthe first top layer and the base layer and the second top layer. 27.Polyolefin film according to claim 1, wherein the thickness of the filmis from about 4 to about 60 μm, the base layer making up from about 40to about 60% of the total thickness.
 28. Polyolefin film according toclaim 27, wherein the thickness of the film is from about 5 to about 30μm.
 29. Polyolefin film according to claim 1, wherein the base layercomprises from about 70 to about 99% by weight of a propylene polymer.30. Polyolefin film according to claim 29, wherein the propylene polymeris propylene homopolymer.
 31. Polyolefin film according to claim 1,wherein the base layer is opaque and comprises vacuole-initiatingfillers.
 32. Polyolefin film according to claim 31, wherein the baselayer further comprises pigments.
 33. Polyolefin film according to claim31, wherein the opaque base layer comprises from about 0.5 to about 30%by weight of vacuole-initiating fillers.
 34. Polyolefin film accordingto claim 31 or 32, wherein the opaque base layer comprises from about 1to about 8% by weight of pigments.
 35. Polyolefin film according toclaim 1, wherein the base layer comprises antistatic.
 36. Polyolefinfilm according to claim 35, wherein the antistatic is tertiary aliphaticamine.
 37. Process for the production of a polyolefin film according toclaim 1 wherein a polymer melt is extruded through a slot die to yield aprefilm and the prefilm is then oriented in the longitudinal directionand the transverse direction, the orientation in the longitudinaldirection is carried out with a longitudinal stretching ratio of from3:1 to 8:1 and in the transverse direction with a transverse stretchingratio of from 5:1 to 10:1.
 38. Packaging film, comprising a polyolefinfilm according to claim 1 and a PVDC or acrylic lacquer or a PVDC oracrylic lacquer coating on the surface of the second top layer. 39.Method of making a roll-wrap packaging which method comprises convertinga film as claimed in claim 1 into a roll-wrap packaging.